Studies on Breeding for High Protein Rice. : I. Protein Content of Different Rice Varieties and Their Relations with Some Agronomic Traits Including Yield

Abstract

Protein content of brown rice of various rice varieties and its relations to agronomic traits were investigated. Statistically significant differences in the protein content of brown rice were observed among cultivars in Japan. The content of protein was approximately 10% higher in brown rice than in polished rice. The protein content was increased by the heavy application of nitrogen. Protein content was nega-tively correlated with the grain yield as well as with the 1000 grain weight, but not correlated with the days to heading and the visual grain quality. A few exceptional cases, however, were observed. For one instance, the two cultivars in the northern part of Japan, “Fukunishiki”and“Fujiminori”, do not differ in their grain yield and heading times, but the former variety contained much more protein than the latter one. For another instance, “Fuku nishiki”and one of the leading varieties in the Japan Sea side area“Honenwase”were both rela-tively high yielding and were top-ranking in the content of protein. An experiment was conducted in order to probe the negative correlation observed between the-protein content and the grain yield.“Kinmaze”is one of high yielding varieties in the central Japan. It contained much less protein than a high protein. mutant N0.217, which bore a small number of grains and was low yielding. The spikelets of“Kinmaze”were clipped to make its sink size equi-valent to that of the mutant strain. Then then the protein content of the high yielding variety was. successfully increased up to the same level as the high protein strain, however, yield was reduced. The reasons for the negative correlation between the above two characters were discussed with reference to the sink and source theory of the carbohydrate and protein accumulation.